1. Field of the Invention
The present invention relates generally to data transfer, and more particularly, to systems for scheduling the transmission of data in a network device.
2. Description of Related Art
Routers receive data on a physical media, such as optical fiber, analyze the data to determine its destination, and output the data on a physical media in accordance with the destination. Routers were initially designed using a general purpose processor executing large software programs. As line rates and traffic volume increased, however, general purpose processors could not scale to meet these new demands. For example, as functionality was added to the software, such as accounting and policing functionality, these routers suffered performance degradation. In some instances, the routers failed to handle traffic at line rate when the new functionality was turned on.
To meet the new demands, purpose-built routers were designed with components, such as a scheduler, optimized for routing. Typical asynchronous transfer mode (ATM) line cards, for example, schedule cells onto a link using a cell scheduler (SAR) that conforms to ATM scheduling disciplines, as defined in the ATM Forum specifications. Conventional SARs do not provide, however, quality of service (QoS) scheduling, such as weighted round robin scheduling, per-packet strict priority scheduling, hierarchical virtual path-virtual circuit scheduling, and the like, which are desirable to Internet Service Providers (ISPs).
Accordingly, it is desirable to improve scheduling in a network device.